The present invention is directed to a variable resistance switch having a plurality of discrete resistance values and which provides a positive feel to the operator as the switch is manually indexed between the values.
Previous dimmer switches, such as those used in automobiles, have utilized a resistance material painted or deposited on a substrate and a pair of wiper arms which were rotated along the resistance material. In this manner, the length of the resistance material generating the resistance value was varied to effect control of the dimming of the lights in the automobile.
However, it has been found that the painted on material may become dirty thereby degrading the electrical contact between the wiper arm and the material or the resistance material may actually erode by mechanical contact with the wiper arm thereby providing dead spots beyond the erosion location. Once the material becomes scratched or contact is less than perfect due to uncleanliness, the switch may essentially become inoperative. Additionally due to the length of the device and since the electrical connection is dependent upon the location where a pair of wiper arms make contact with the resistance material, the linearness of the overall device is in question.
The use of a resistor network as provided herein provides for enhanced control of the dimming function. A thick film resistor network having sufficient electrical resistance to dim the interior lights of an automobile is used. The resistor network may be of variable thickness and sizes and may be wave soldered to a printed circuit board. Custom resistance values are values that are accomplished by laser trimming the resistor network, thus the dimming characteristics can be precisely controlled either to be linear or nonlinear.
Additionally providing a resistor network with discrete steps enhances reliability, stability, accuracy, and most importantly, repeatability of the networks ensures uniformity from switch assembly to switch assembly. Conventional printed resistors or potentiometers exhibit only some of these traits and may have flat or dead spots which are undesirable.
Additionally, the sensitivity of customary resistors can be designed out of the switch using the resistor network. By providing for discrete energization of various portions of the resistor network, the electrical performance of the switch becomes highly repeatable. Furthermore, a positive feel may be provided to the operator by the provision of a series of mini-detents which transmit positive feedback to the operator as the switch is indexed. The use of the mini-detents may also be coordinated with the separate discrete values of the resistor network such that the operator may feel the detent follower index from detent to detent as the switch is indexed from detent to detent and as simultaneously the resistor network is indexed between values. Hence, a particular detent may be aligned with a particular resistance value such that as the switch is rotated to that detent, the appropriate electrical contacts are made to obtain the desired resistance value. Hence, the positioning of the switch may be repeated from switch to switch and is not dependent upon the accuracy and thickness of a deposited, painted on layer of resistance material.
U.S. Pat. No. 4,613,733 describes a delay wiper switch using a resistance network. This patent, which is commonly assigned with the herein application, discloses the use of a resistor network for determining selected resistance values for use in controlling windshield wipers. This patent although disclosing a detent mechanism does not disclose a detent mechanism for indexing between the various resistance values of the resistance network.